1. Field of the Invention
The present invention relates generally to electrical circuits, and more particularly but not exclusively to ripple reducers.
2. Description of the Background Art
As its name implies, a ripple reducer is an electrical circuit for reducing a ripple of a signal. In a light emitting diode (LED) lighting circuit, a ripple reducer is employed to reduce the ripple of an LED current through an LED array. The ripple reducer may comprise a linear regulator that senses the LED current from a sense resistor and drives a metal oxide semiconductor field effect transistor (MOSFET) to regulate and smooth the LED current. A problem with this ripple reducer topology is that the sense resistor increases the power loss of the LED lighting circuit. Another ripple reducer topology comprises a linear regulator that drives a bipolar junction transistor (BJT), instead of a MOSFET. The BJT does not require a sense resistor but has severe power loss due to the collector-to-emitter voltage of the BJT in the active region, because it is relatively difficult to automatically optimize the saturation voltage of the BJT.